This invention relates to a method of completing a well that penetrates a subterranean formation and more particularly relates to a well completion technique wherein an inside-the-casing consolidated gravel pack is formed within the well to control the production of sand from the formation.
In completing a well that is drilled into the earth and penetrates a subterranean fluid-bearing formation, a string of casing is often run into the well and a cement slurry flowed into the annulus between the casing string and the wall of the well and allowed to set and form a cement sheath to bond the casing to the wall of the well. A perforating means may be lowered into the well adjacent the fluid-bearing formation of interest and activated to perforate the casing and cement sheath and provide perforation tunnels which communicate between the interior of the well and the subterranean formation.
The subterranean formation may be an unconsolidated or loosely consolidated formation or may essentially be a consolidated formation having streaks or zones of friable material. When fluids such as oil or gas are produced from such formations, the produced fluids may carry entrained therein formation material, hereinafter referred to as "sand". The production of sand from a formation into a well is undesirable for many reasons. It is abrasive to components found within the well such as tubing, pumps and valves and must be removed from the produced fluids at the surface.
Various techniques have been used to control the production of sand from subterranean formations. Two commonly used techniques are gravel packing and formation consolidation techniques. Gravel packing involves generally the placement of gravel within a well adjacent a formation from which fluids are to be produced to form a gravel filter. In a cased perforated well the gravel may be placed inside the casing adjacent the perforations to form an inside-the-casing gravel pack or may be placed outside the casing and adjacent the formation or may be placed both inside and outside the casing. The gravel may be consolidated by use of consolidating materials to better hold it in place. Techniques for forming gravel packs and inside-the-casing consolidated gravel packs are well known. For example, in U.S. Pat. No. 3,621,915 there is described a method of providing sand control of underground formations penetrated by a well by forming an epoxy resin consolidated sand or gravel pack of high compressive strength in the well. A description of inside gravel packing methods is given in an article entitled "Sand Control", Part 5 -- Inside Gravel Packing, by George O. Suman, Jr., World Oil, pp. 67-76, March 1975. Suman there points out that careful gravel packing of perforations as well as the screen-casing annulus assures maximum benefit from gravel placement jobs inside casing.
Formation consolidation techniques of sand control involves generally the injection of sand consolidation chemicals into unconsolidated formations to consolidate the formations in situ. The sand consolidation chemicals often used include Phenol resin, Phenol-formaldehyde, Epoxy, Furan and Phenolicfurfuryl. In Part 7 of the aforementioned "Sand Control" article entitled "Consolidating Formation by Chemical Methods Requires Precise Application and, Careful Fluid Handling", published in World Oil, pages 75-83, May 1975, there is tabulated available systems for consolidating formations in place or for packing perforations with resincoated gravel slurries.
In a two-part article by J. L. Rike entitled "Shortcomings of Present Sand-Control Methods Suggest New Fail-Safe Concept -- 1", The Oil and Gas Journal, pages 97-102, Feb. 17, 1975, and "Shortcomings Suggest New Fail-Safe Concept", The Oil and Gas Journal, pages 76-80, Feb. 24, 1975, there is described a new fail-safe concept that has been developed for sand control in high-rate wells and for stimulation of unconsolidated sands. The method uses a specifically designed screen and quite large gravel placed with a prior treatment of consolidating plastic. A resin material is first introduced into the formation before the well is gravel-packed with large gravel. The resin consolidates the formation sand that remains in direct contact with the pack gravel after the job is completed. The use of large gravel maximizes productivity throughout the gravel-packed interval and especially in the perforation tunnels. The pack gravel need not be sized to bridge the formation sand since the formation sand has been consolidated in the region where invasion would occur. A screen is used with the gravel pack that is sized to stop the entry of formation sand rather than sized to hold back the pack gravel. This makes the system fail-safe from the standpoint of formation-sand production.
In U.S. Pat. No. 3,826,310 there is described a well treatment technique for sand control. The well is treated by injecting a slurry of packing grains, self-curing resin, and carrier liquid to form a permeable resin-consolidated mass of grains in or around a cased and perforated section of well casing ahead of a fluid-transported mass of solid particles that have a size and composition adapted to form chemically removable plugs across the openings of casing perforations that have been filled with the slurry. Substantially all of the slurry is displaced from the casing interior into the perforations in the perforated section of the casing. After allowing the resin-consolidated packs to cure, the chemically removable plugs are removed, e.g. by circulating a plug-dissolving fluid into the well until at least enough of the plugging particles are dissolved to provide passageways into the perforations.